Electronically commutable motor

ABSTRACT

An electronically commutatable motor, whose excitation windings are controllable via semiconductor output stages by an electronic control unit with the aid of PWM control signals, a setpoint value being specifiable to the control unit, and the control unit emitting corresponding PWM control signals to the semiconductor output stages. The start-up of the motor is monitored in a simple manner and an overloading is prevented in that, with the input of the setpoint value and/or the switching on of the control unit and/or the semiconductor output stages, after a predefined or predefinable starting time has expired, a monitoring device monitors the speed of the motor to check whether a minimum speed has been reached, and if the minimum speed is not reached, the control unit and/or the semiconductor output stages is/are disconnectible.

FIELD OF THE INVENTION

The present invention relates to an electronically commutatable motor,whose excitation windings are controllable via semiconductor outputstages by an electronic control unit with the aid of PWM controlsignals, a setpoint value being specifiable to the control unit, and thecontrol unit emitting corresponding PWM control signals to thesemiconductor output stages; and a monitoring device for the speed ofthe motor is provided with which a faulty movement or a standstill ofthe motor is detectable, and the motor is able to be switched off.

BACKGROUND INFORMATION

U.S. Pat. No. 5,349,276 describes an electronically, commutatable motorof this type. In this known motor, the speed (=rpm) is predefined andmonitored within a specific framework of minimum to maximum rpm. If thisframework is left, the engine is switched off. Thus, an immediate andquick detection of the proper revolution, and specifically as a functionof a predefined setpoint value of the rpm, is not possible. Ifdifficulties—sluggishness or locking of the motor—occur during thestart-up, the motor can become overloaded and damaged before it getswithin the monitored speed range.

Such motors are used for various application cases. Depending upon thetype of construction, these motors have a plurality of stop locationswhich frequently bring with them difficulties for the start-up of themotor, and can result in the motor not starting up, even in response tothe input of a setpoint value. In addition, mechanical faults may existthat result in a locking of the motor at standstill, which can lead tooverloading upon application of a setpoint value at the control unit.

U.S. Pat. No. 5,682,334 deals with a start-up monitoring of the motor,which, however, does not work with predefined fixed values, but ratherhas stored a predetermined acceleration characteristic that is definedby points of time and speed. The monitoring is carried out in the mannerthat a reached motor speed =rpm and the time elapsed since the beginningof the start-up are compared to the time allocated for this speed in thestored characteristic. In this context, the same start-up conditions anda defined preset start-up characteristic are assumed; however, in manycases the motor is put into operation with different start-up conditionsfor different operating states. This is not easily possible using theknown start-up monitoring.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an electronicallycommutatable motor of the type mentioned at the outset, in whichmonitoring is already carried out at the beginning of the start-up inorder to avoid overloading and damage due to overloading.

This objective is achieved according to the present invention in that,when the motor is put into operation by input of a setpoint value and/orswitching on the control unit and/or the semiconductor output stages, astart-up time is specifiable to the monitoring device, the start-up timebeing a function of the magnitude of the predefined setpoint value andpreferably increasing as the magnitude of the setpoint value increases,and after the predefined start-up time has elapsed, the monitoringdevice compares the speed reached by the motor to a minimum speed, andif the minimum speed is not reached, switches off the control unitand/or the semiconductor output stages.

Decisive is a start-up time Tx which is a function of setpoint valueN_(setpoint) predefined for the start-up, and therefore takes intoaccount the different start-up characteristic curves. Only after thistime is it determined whether achieved speed N of the motor has reacheda predefined minimum speed N_(min). By appropriate selection of thepredefined start-up times Tx, comparison can continually be made to thesame minimum speed N_(min). The monitoring expenditure necessary forthis is minimal.

According to one embodiment, the control unit and/or the semiconductoroutput stages can be switched on and off simply by switching the supplyvoltage on and off.

In addition, the switch-off of the control unit and/or the semiconductoroutput stages, and thus of the motor, may be time-delayed.

According to a further embodiment, the missing and/or faulty start-up isable to be indicated visually and/or acoustically.

If the monitoring unit and/or the display device is/are integrated intothe control unit, then the structural design of the motor does notchange, since the electronic control unit also takes over the functionsof the monitoring device.

BRIEF DESCRIPTION OF THE DRAWING

The FIG. 1 is a block diagram illustrating an exemplary embodimentaccording to the present invention.

DETAILED DESCRIPTION

The motor unit includes the following functional units: control unitSTE, semiconductor output stages EST and actual motor M having theexcitation windings of the stator and having the permanent-magnet rotorwhich may be constructed as an external or internal rotor.

If motor M is to be put in operation, then a setpoint valueN_(setpoint), which is intended to lead to a speed N of motor M, isspecified to control unit STE. For example, the setpoint selection maybe preselected manually via a potentiometer. In control unit STE, afunction is predefined which contains the dependence of PWM controlsignals PWM_(end) for semiconductor output stages EST on speed setpointvalue N_(setpoint).

With the switching on of control unit STE and/or of semiconductor outputstages EST, a start signal Te is emitted to a monitoring device UE whichdetects speed N of motor M in a generally known manner.

After a predefined starting time Tx, monitoring device UE, inconjunction with control unit STE, checks whether a predeterminedminimum speed N_(min) has been reached. If this is the case, then thestart-up of motor M is continued and carried on up to the continuousoperation with the predefined setpoint speed.

However, if monitoring device UE and/or control unit STE determines thatmotor M has not started up at all, or corresponding minimum speedN_(min) has not been reached in predefined starting time Tx, then, toprotect against overloading, control unit STE and/or semiconductoroutput stages EST are switched off, as the contacts “off” for switchingoff supply voltage U_(batt) indicate.

Control unit STE is able to alter the pulse width and/or the commutationfrequency of PWM control signals PWM_(end) as a function of setpointvalue N_(setpoint).

With increasing setpoint value N_(setpoint), starting time Tx maylikewise increase. However, it is always short enough to preventoverloading of the motor and its electronic components. Naturally, thisis also applicable when control unit STE and/or the semiconductor outputstages is/are switched off in a time-delayed manner.

The missing and/or faulty start-up of the motor may be displayedvisually and/or acoustically, or electrically via the setpoint-valueline.

Monitoring device UE and/or the display device are preferably integratedwith their functions into control unit STE.

What is claimed is:
 1. An electronically commutatable motor, comprising:a plurality of excitation windings; a plurality of semiconductor outputstages; a control unit for controlling the plurality of excitationwindings via the plurality of semiconductor output stages in accordancewith PWM control signals and for emitting the PWM control signals to theplurality of semiconductor-output stages, a setpoint value beingspecificable to the control unit; and a monitoring device for monitoringa speed of the electronically commutatable motor and for detecting oneof a faulty movement of the electronically commutatable motor and astandstill of the electronically commutatable motor, wherein: when theelectronically commutatable motor is operated by at least one of aninput of the setpoint value and a switching on of at least one of theelectronically commutatable motor and the plurality of semiconductoroutput stages, a start-up time is specificable to the monitoring device,the start-up time is a function of a magnitude of the setpoint value,after an elapsing of the start-up time, the monitoring device comparesthe speed of the electronically commutatable motor to a minimum speed,and the monitoring device switches off the electronically commutatablemotor if the minimum speed is not reached.
 2. The electronicallycommutatable motor according to claim 1, wherein: the control unit emitsto the plurality of semiconductor output stages one of the PWM controlsignals tuned in one of a pulse width and a commutation frequency to thesetpoint value.
 3. The electronically commutatable motor according toclaim 1, wherein: the switching on of the electronically commutatablemotor is effected by switching on a supply voltage, and the switchingoff of the electronically commutatable motor is effected by switchingoff the supply voltage.
 4. The electronically commutatable motoraccording to claim 1, wherein: a switch-off of at least one of thecontrol unit and the plurality of semiconductor output stages occurs ina time-delayed manner.
 5. The electronically commutatable motoraccording to claim 1, wherein: at least one of the faulty movement ofthe electronically commutatable motor and the standstill of theelectronically commutatable motor is presented at least one of visuallyand acoustically.
 6. The electronically commutatable motor according toclaim 1, wherein: at least one of the monitoring device and a displaydevice is integrated into the control unit.
 7. The electronicallycommutatable motor according to claim 1, wherein: the start-up timeincreases as the magnitude of the setpoint value increases.